Feature-based process planning using STEP-NC

To survive in the global market, companies must integrate CAD, CAM and CNC so as to make products of higher quality with lower cost and shorter lead times. Traditionally, NC programming for machine tools is normally done by using G-code (ISO 6983 Numerical control of machines -- Program format and definition of address words -- Part 1: Data format for positioning, line motion and contouring control systems). G-code focuses on the path of the cutter location (CL) and lacks most product and process information, such as the geometrical and topological information, part materials, tolerance and etc. To solve the above problems, a new ISO standard known as STEP-NC, which extends STEP standard to NC, is being developed, including STEP-NC ARM (Application Reference Model) as the ISO 14649, and AIM (Application Information Model) mapping the STEP-NC ARM as the ISO 10303 AP238. This paper presents a framework for seamless integration between CAD/CAM and CNC by incorporating STEP-NC, feature technology and object-oriented techniques. After a brief introduction, a literature review of the current state of STEP-NC is given. Then, the proposed framework is described, including: 1) a feature-based model for STEP-NC, which includes not only the geometrical and topological information, but also information related to manufacture, such as machining features, machining operations and tools; 2) a information model for manufacturing process using the structure defined in ISO 10303-21 (Implementation methods: Clear text encoding of the exchange structure); and 3) an architecture for bi-directional transformation of CAD/CAM and NC machines. Finally, the conclusions are drawn and further research is summarised.